1. Field of the Invention
The present invention relates to mobile tethers providing a physical connection between two locations. More specifically, the present invention relates to a system and method for providing an actuated tether capable of moving itself, remaining free while traversing around obstacles, and/or freeing itself when pinned by debris or restrained by obstacles.
2. Description of the Related Art
A longstanding goal of mobile robotics is to allow robots to work in hazardous or inaccessible environments. Post-disaster urban search and rescue is one of the most hazardous environments imaginable, and victims are often in unreachable locations buried beneath unstable rubble. The goal of rescue robotics is to extend the capabilities of human rescuers while also increasing their safety. Robots can enter voids too small or deep for humans and can survey larger voids that humans are not permitted to enter until, for example, a fire has been put out or a structure has been reinforced. They can carry various types of equipment, such as thermal imagers, cameras, hazardous materials sensors, medical supplies, or even food and water into the interior of a rubble pile far beyond where searchers may otherwise reach, such as with a boroscope.
In practice, however, rescue robots have encountered a number of difficulties involving radio transmission inefficiency, poor maneuverability, and tethers becoming caught. Numerous publications have discussed experiences with rescue robots at actual disaster sites. One such publication is “Human-Robot Interactions during the Robot-Assisted Urban Search and Rescue Response at the World Trade Center,” Casper, J., and Murphy, R. R., IEEE Transactions on Systems, Man and Cybernetics Part B, Vol. 33, No. 3, pp. 367-385, June 2003, which is hereby incorporated by reference in its entirety.
Rescue robots may come in many forms and varieties. Robots likewise may be polymorphic, meaning that the robot's effectors (components that perform actuation and any connections relating to those components) may be dynamically changed to fit the environment. Some examples of existing robots are listed Table I in “How UGVs Physically Fail in the Field,” Carlson, J., and Murphy, R. R., submitted IEEE Transactions on Robotics for publication and publicly available at crasar.csee.usf.edu/research/Publications/CRASAR-TR2004-16.pdf, which is hereby incorporated by reference in its entirety. The robots may be of a variety of different sizes, may use different means of locomotion, may use different types of power, may have different modes of control, may incorporate different tools or equipment, and may have different modes of communication. Some examples of robot types and features are described in “Human-Robot Interaction in Rescue Robotics,” Murphy, R., IEEE Systems, Man and Cybernetics Part C: Applications and Reviews, special issue on Human-Robot Interaction, Vol. 34, No. 2, May 2004, which is hereby incorporated by reference in its entirety.
In many environments in which rescue robots may be needed, however, the most useful robot size is about the dimensions of a shoebox. This limitation in size can preclude use of certain types of controls that, for example, may require multiple sensors, certain types of power such as batteries, or certain means of locomotion.
Reliability of the rescue robots obviously is an important issue. Rescue robots can fail for a wide variety of reasons. Examples of rescue robot failures are described and discussed in the previously referenced articles and in other published articles such as “Follow-up Analysis of Mobile Robot Failures,” J. Carlson, R. Murphy, A. Nelson, IEEE International Conference on Robotics and Automation (ICRA), April 2004, which is hereby incorporated by reference in its entirety.
Communication has been a large issue with respect to rescue robots. Wireless robots typically are larger and more mobile than tethered robots, but they still require a safety line and communication are easily lost in the harsh environment in which they are used. For example, following the World Trade Center disaster on Sep. 11, 2001, a communication failure caused the temporary loss of an untethered, teleoperated robot. As such a disaster site, usable communication frequencies are very limited because most frequencies are reserved for emergency response agents. Additionally, thick concrete walls and steel debris often obstruct radio communication between the operator and the robot. These communications difficulties often make tethered robots more reliable and useful than untethered robots in this kind of environment.
Tethered robots additionally may be much smaller than their untethered counterparts due to the elimination of batteries and wireless communications equipment. A smaller size allows tethered robots to search areas that would be inaccessible by larger robots.
Lack of mobility also can hinder robotic search and rescue efforts. For example, it is often beneficial to deploy robots through holes or vertical pipes. Tethers are beneficial in these situations as tethered robots can be safely lowered or raised vertically. Additionally, in the event of a robot malfunction, tethers may be used for robot recovery.
Drawbacks of using conventional tethers include increased drag and a tendency to catch on obstacles. Conventional tethers therefore may limit the depth and path of exploration. The use of tethers also requires an additional operator to handle the tether. This operator attempts to avoid breaking or locking the tether on debris as the robot moves into the site. Tether managers, of course, are at risk since they often work close to structures with questionable stability during the deployment.
Many of these issues also pertain to other applications of remotely controlled vehicles in inaccessible or hazardous locations. For example, vehicles for pipe inspection and repair or military operations in trenches and caves encounter similar problems with communications and tether management. Examples of such other applications are disclosed in U.S. Pat. Nos. 6,697,710 and 4,862,808, which are hereby incorporated by reference in their entirety. The present invention described below is equally applicable to these other applications in addition the field of rescue robots.